minor updates.

dbms/src/Columns/IColumn.h

@@ -24,20 +24,6 @@ namespace ErrorCodes
 class Arena;
 class ColumnGathererStream;
 
-struct ColumnSize
-{
-    size_t marks = 0;
-    size_t data_compressed = 0;
-    size_t data_uncompressed = 0;
-
-    void add(const ColumnSize & other)
-    {
-        marks += other.marks;
-        data_compressed += other.data_compressed;
-        data_uncompressed += other.data_uncompressed;
-    }
-};
-
 /// Declares interface to store columns in memory.
 class IColumn : public COW<IColumn>
 {

dbms/src/Storages/IStorage.h

@@ -38,6 +38,19 @@ class AlterCommands;
 class MutationCommands;
 class PartitionCommands;
 
+struct ColumnSize
+{
+    size_t marks = 0;
+    size_t data_compressed = 0;
+    size_t data_uncompressed = 0;
+
+    void add(const ColumnSize & other)
+    {
+        marks += other.marks;
+        data_compressed += other.data_compressed;
+        data_uncompressed += other.data_uncompressed;
+    }
+};
 
 /** Storage. Describes the table. Responsible for
   * - storage of the table data;
@@ -82,6 +95,8 @@ public:
     /// Returns true if the storage supports deduplication of inserted data blocks.
     virtual bool supportsDeduplication() const { return false; }
 
+    /// Optional size information of each physical column.
+    /// Currently it's only used by the MergeTree family for query optimizations.
     using ColumnSizeByName = std::unordered_map<std::string, ColumnSize>;
     virtual ColumnSizeByName getColumnSizes() const { return {}; }
 

dbms/src/Storages/MergeTree/MergeTreeDataPart.h

@@ -22,6 +22,7 @@
 namespace DB
 {
 
+struct ColumnSize;
 class MergeTreeData;